Westoco type fuel pump

ABSTRACT

To make a Wesco type fuel pump to supply pressure-increased fuel toward a fuel injection valve with no time delay at a time of restarting an engine with an excellent restarting property, an impeller ( 8 ) which is rotated by an electric motor (M) arranged within a motor chamber ( 9 ) is arranged within a pump chamber ( 7 ), a fuel inflow passage ( 6 ) which communicates with the outside and a discharge hole ( 5 ) which communicates with the motor chamber ( 9 ) are open to the pump chamber ( 7 ), and the discharge hole ( 5 ) is provided with a fuel holding function which inhibits air from flowing into the motor chamber ( 9 ) from the pump chamber ( 7 ) at a time when the engine stops.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a fuel pump mounted on a motorvehicle, a motor cycle and the like, and more particularly to a Wescotype fuel pump which deliver fuel by generating a pressure differencebetween the front and the rear of a blade groove provided in an outerperiphery of an impeller arranged within a pump chamber by rotation ofthe impeller by means of an electric motor, and increasing pressure ofthe fuel by continuously increasing the pressure difference.

TECHNICAL BACKGROUND OF THE INVENTION

[0002] A conventional Wesco type fuel pump is shown in JapaneseUnexamined Patent Publication No. 7-197896.

[0003] In accordance with this structure, the Wesco type fuel pump(hereinafter, simply referred to as a fuel pump) is constituted by apump portion and an electric motor.

[0004] A pump housing and a pump cover opposingly connected with thepump housing are arranged in a lower side of a housing formed in acylindrical shape, and these elements are arranged fixedly in a lowerside of the housing.

[0005] The cylindrical pump chamber is formed by a closed-end circularrecess portion which is provided in the pump housing and has an openlower side, and a pump cover flat portion which closes the circularrecess portion. A fuel inflow passage being open downward and adischarge hole being open toward the inside of a motor chamber formedwithin the housing are formed in the pump chamber. An impellercorresponding to a turbine vane formed in a disc shape is rotatablyarranged within the pump chamber, a plurality of blade groovescommunicating the top and back sides of the impeller are provided in anouter peripheral portion of the impeller, the impeller is connected to arotating shaft of the electric motor arranged within the motor chamber,and the impeller rotates within the pump chamber on the basis of therotation of the electric motor.

[0006] Further, a fuel flow passage which faces to the blade grooves ofthe impeller, is open to the inside of the pump chamber and is in acircular arc shape is provided in a depressed shape in a lower surfaceof the pump housing forming the pump chamber, and the discharge hole isprovided so as to be open to the fuel flow passage in a terminal endportion in a rotational direction of the impeller. On the other hand, afuel flow passage which faces to the blade grooves of the impeller, isopen to the inside of the pump chamber and is in the circular arc shapeis provided in a depressed shape in an upper surface of the pump coverforming the pump chamber, and the fuel inflow passage is provided so asto be open to the fuel flow passage in a starting end portion in therotational direction of the impeller.

[0007] In accordance with the fuel pump mentioned above, an electriccurrent is applied to the electric motor and the electric motor isrotated, whereby the impeller rotates within the pump chamber, and apressure difference is generated between the front and the rear of theblade groove of the impeller. The fuel is sucked into the pump chamberincluding the fuel flow passage through the fuel inflow passage byrepeating the action mentioned above by means of a lot of blade grooves,and the pressure increased fuel is discharged from the pump chamber intothe motor chamber via the discharge hole.

[0008] Further, the pressure increased fuel supplied within the motorchamber opens a check valve within the fuel discharge passage being opento the upper portion of the housing on the basis of the fuel pressure,and is supplied toward an external fuel injection valve.

[0009] On the other hand, in the Wesco type fuel pump mentioned above,there is provided with an air bleeding hole for preventing a vapor lockwithin the pump chamber, and this structure is disclosed in JapaneseUnexamined Patent Publication No. 9-209864.

[0010] In this case, an upper side of the air bleeding hole is formed soas to be open to the pump chamber via the fuel flow passage provided inthe pump cover, and a lower side thereof is provided so as to be openoutward from the pump cover.

[0011] Accordingly, a vapor generated within the pump chamber isdischarged out of the pump chamber via the air bleeding hole togetherwith the pressure increased fuel (corresponding to only a small part ofthe fuel) within the pump chamber, and it is possible to prevent thevapor lock from being generated within the pump chamber.

[0012] In accordance with the conventional Wesco type fuel pumpmentioned above, in the case that the fuel pump is arranged within thefuel tank, and a fuel liquid surface formed within the fuel tank islower than an opening of the fuel inflow passage formed in the pumpcover, the following problems are generated.

[0013] In the case that the fuel pump is stopped in accordance with anengine stop in the state mentioned above, the check valve within thefuel discharge passage provided in the upper portion of the housingautomatically closes the fuel discharge passage on the basis of adisappearance of the fuel pressure applied outward, and prevents thefuel within the downstream side of the fuel pipe than the check valvefrom flowing back toward the inside of the fuel pump.

[0014] On the other hand, in the state mentioned above, the fuel liquidsurface within the fuel tank exists at a lower position than the loweropening of the fuel inflow passage and the lower opening of the airbleeding hole, whereby the air existing above the fuel liquid surfaceflows into the pump chamber from the air bleeding hole, and the fuelexisting within the pump chamber is discharged into the fuel tank viathe fuel inflow passage. Further, the air flowing into the pump chamberin the manner mentioned above flows into the motor chamber via the bladegrooves of the impeller, the fuel flow passage of the pump housing andthe discharge hole, the air is replaced by the fuel within the motorchamber gradually, and the fuel within the motor chamber is dischargedinto the fuel tank via the discharge hole, the pump chamber and the fuelinflow passage.

[0015] In accordance with the structure mentioned above, there is a riskthat the motor chamber becomes empty without fuel in accordance with apassage of time after the engine stops.

[0016] Further, in the case that the engine starting operation is againcarried out and the fuel pump is driven, in the state of no fuel withinthe motor chamber, the fuel discharged from the pump chamber via thedischarge hole first fills up the motor chamber with the fuel so as toincrease the pressure, and is thereafter supplied toward the fuelinjection valve from the fuel discharge passage.

[0017] A remarkable matter here is that a volumetric capacity of themotor chamber is far larger than a volumetric capacity of the pumpchamber. In other words, the motor chamber having the larger volumetriccapacity is first filled with the fuel upon restarting the engine, longtime is required until the fuel pressure within the motor chamber isincreased, and the fuel supply to the fuel injection valve is delayed,so that there is a risk that an good restarting property of the engineis hampered.

[0018] Further, in the case that the fuel pump is arranged within thevarious fuel tanks, the fuel pump may be arranged in all directions suchas in a vertical direction, a diagonal direction and a horizontaldirection in view of a layout of the fuel pump. Therefore, differencesoccur in an air inflow into the pump chamber from the air bleeding holeaccording to the various arrangement states mentioned above, residualfuel within the pump chamber is uneven, and it is impossible to obtain astable engine restarting property.

[0019] On the other hand, in accordance with Japanese Unexamined PatentPublication No. 2001-27160, there is disclosed a structure in which thecheck valve is arranged in the discharge hole, and the pressure withinthe motor chamber is held at a time when the fuel pump is stopped.However, in accordance with this structure, the number of parts andassembling man-hours are increased, whereby it is impossible to reduce amanufacturing cost, and it is hard to design the arrangement of thecheck valve within a narrow discharge hole.

SUMMARY OF THE INVENTION

[0020] A Wesco type fuel pump in accordance with the present inventionis made by taking the problems mentioned above into consideration, and amain object of the present invention is to provide a Wesco type fuelpump which can immediately supply fuel pressured increasedly by a fuelpump toward a fuel injection valve particularly upon restarting anengine after stopping the engine, and can obtain an improved and stableengine restarting property.

[0021] In order to achieve the object mentioned above, in accordancewith a first aspect of the present invention, there is provided a Wescotype fuel pump comprising:

[0022] a pump chamber which is formed of a pump housing and a pump covercovering the pump housing;

[0023] an impeller which is rotatably arranged within the pump chamber,is rotated by an electric motor within the motor chamber, and isprovided with a plurality of blade grooves communicating the top andback sides in an outer periphery thereof; and

[0024] a discharge hole which has a fuel flow passage provided in adepressed shape in a peripheral direction along the blade grooves of theimpeller on a lower surface facing to the pump chamber of the pumphousing, and is formed in a terminal end portion in a rotationaldirection of the impeller so as to communicate the pump chamber with themotor chamber,

[0025] wherein the discharge hole is provided with a fuel holdingfunction of inhibiting air from flowing into the motor chamber from thepump chamber on the basis of surface tension of the fuel, at a time whenthe fuel pump is stopped.

[0026] Further, in accordance with a second aspect of the presentinvention, in addition to the first aspect mentioned above, thedischarge hole is open in the lower surface of the pump housing with astep portion facing to the pump chamber.

[0027] Further, in accordance with a third aspect of the presentinvention, in addition to the first aspect mentioned above, an openingarea of the discharge hole is made smaller toward the front side in arotational direction of the impeller.

[0028] Further, in accordance with a fourth aspect of the presentinvention, in addition to the second aspect mentioned above, the stepportion is formed in a similar shape to the discharge hole.

[0029] In accordance with the first aspect of the present invention, ina state in which the fuel within the pump chamber is discharged to theoutside via the fuel inflow passage and the air is flowed into the pumpchamber, at a time when the fuel pump is stopped in accordance with theengine stop, a fuel film serving as the fuel holding function caused bythe surface tension of the fuel within the motor chamber is formed inthe opening end portion to the pump chamber corresponding to the ambientair side of the discharge hole.

[0030] In accordance with the structure, since the inflow of the airwhich is going to move toward the inside of the motor chamber from theinside of the pump chamber is inhibited by the fuel film formed by thesurface tension, the replacing operation between the air and the fuelwithin the motor chamber does not occur, the fuel within the motorchamber is not discharged into the fuel tank via the discharge hole, thepump chamber and the fuel inflow passage, and it is possible to reserveand hold the fuel within the motor chamber. Accordingly, no delay iscaused in the fuel supply toward the fuel injection valve at a time ofrestarting the engine, and it is possible to obtain an improved enginerestarting property.

[0031] Further, in accordance with the second aspect of the presentinvention, since the lower end of the discharge hole is open in thelower surface of the pump housing with the step portion, the fuel filmis not brought into contact with the impeller arranged within the pumpchamber even in the case that the fuel film is formed by the surfacetension in the lower end of the discharge hole so as to be curveddownward. Accordingly, it is possible to securely form the fuel film.

[0032] Further, in accordance with the third aspect of the presentinvention, since the opening area of the discharge hole is formednarrower toward the front side in the rotational direction of theimpeller, the fuel film is formed from the narrower portion, so that itis possible to securely form the fuel film.

[0033] Further, in accordance with the fourth aspect of the presentinvention, since the step portion is formed in the similar shape to thedischarge hole, it is possible to make the step portion compact.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a vertical cross sectional view of a Wesco type fuelpump in accordance with the present invention;

[0035]FIG. 2 is a plan view of a pump housing used in FIG. 1 as seenfrom the lower side;

[0036]FIG. 3 is a vertical cross sectional view of a main portion alonga line X-X in FIG. 2; and

[0037]FIG. 4 is a plan view of a pump cover used in FIG. 1 as seen fromthe upper side.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0038] A description will be given below of an embodiment of a Wescotype fuel pump in accordance with the present invention with referenceto FIG. 1.

[0039] Reference numeral 1 denotes a tubular housing which is open inupper and lower sides. The upper opening is closed by a first closingmember 2A and a second closing member 2B.

[0040] Specifically, the first closing member 2A and the second closingmember 2B are arranged so as to be brought into contact on an upperlocking step portion 1A of the housing 1, and an upper end of thehousing 1 is caulked inward toward a shoulder portion of the secondclosing member 2B. Further, a fuel discharge passage 2C, in which alower end is open to the inside of the housing 1 and an upper end isopen upward, is formed in the first and second closing members 2A and2B, and a pressure response type check valve 2D which opens the fueldischarge passage on the basis of the fuel pressure applied upward fromthe lower side is arranged in the fuel discharge passage 2C.

[0041] Further, a bearing G which rotatably supports an upper end of anelectric motor mentioned below is arranged in the center of the firstclosing member 2A, and a power source connector 2E for feeding a powerto an armature of the electric motor from the external is provided inthe second closing member 2B.

[0042] Further, the lower opening of the housing 1 is closed by a pumphousing 3 and a pump cover 4.

[0043] The pump housing 3 is well shown in FIG. 2, and is described withusing FIG. 1 together.

[0044] The pump housing 3 is formed in a solid cylindrical shape, and isstructured such that a circular recess portion 3B is provided upwardfrom a lower end 3A, and the bearing G is arranged within a through holein a center portion thereof.

[0045] Further, a circular arc fuel flow passage 3D is provided in adepressed shape in a lower surface 3C of the recess portion, and adischarge hole 5 is provided through in a terminal end portion 3E of thefuel flow passage 3D in a rotational direction A of the impellermentioned below so as to penetrate from the lower surface 3C side towardan upper surface 3F.

[0046] The discharge hole 5 is well shown in FIG. 3.

[0047] The pump cover 4 is well shown in FIG. 4, and is described withusing FIG. 1 together.

[0048] The pump cover 4 is formed in a solid cylindrical shape, and hasa flat surface 4A, which is brought into contact with the lower end 3Aof the pump housing 3 so as to close the opening of the recess portion3B, in an upper portion thereof. A fuel flow passage 4B opposing to thefuel flow passage 3D of the pump housing 3 is provided in a depressedshape in the flat surface 4A, and a fuel inflow passage 6 open towardthe outside of the pump cover 4 is provided in a starting end portion 4Cof the fuel flow passage 4B in the rotational direction A of theimpeller mentioned below.

[0049] Further, reference symbol 4D denotes an air bleeding hole opentoward the outside of the pump cover 4 from the fuel flow passage 4B.

[0050] In this case, FIG. 2 is a plan view of the pump housing 3arranged in the manner shown in FIG. 1 as seen from the lower side, FIG.3 is a vertical cross sectional view of a main portion along a line X-Xin FIG. 2, and FIG. 4 is a plan view of the pump cover 4 arranged in themanner shown in FIG. 1 as seen from the upper side.

[0051] Further, the pump housing 3 is arranged so as to be brought intocontact with the lower locking step portion 1B of the housing 1, and theflat surface 4A of the pump cover 4 is arranged so as to be brought intocontact with the lower end 3A of the pump housing 3, and the lower endof the housing 1 is caulked inward toward the shoulder portion of thepump cover 4 in this state, whereby the pump housing 3 and the pumpcover 4 are arranged so as to be fixed to the lower end of the housing1.

[0052] In accordance with the structure mentioned above, the circularrecess portion 3B of the pump housing 3 is closed by the flat surface 4Aof the pump cover 4 so as to form the pump chamber 7, and the impeller 8is rotatably arranged within the pump chamber 7.

[0053] The impeller 8 is provided with a plurality of blade grooves 8Awhich communicate the top and back sides of the impeller 8 and face tothe fuel flow passage 3D of the pump housing 3 and the fuel flow passage4B of the pump cover 4, on an outer periphery thereof, and a segmentalhole 8B formed in a D shape is provided through in the center thereof.

[0054] On the other hand, a motor chamber 9 is formed within the housing1 between the first closing member 2A and the pump housing 3, and anelectric motor M is arranged within the motor chamber 9.

[0055] The electric motor M is constituted by an armature 10, a rotatingshaft 11 fixedly provided through the center of the armature 10, and apair of permanent magnets 12 facing to an outer periphery of thearmature 10.

[0056] Further, an upper end of the rotating shaft 11 is rotatablysupported to the bearing G of the first closing member 2A, a lower sideof the rotating shaft 11 is rotatably supported to the bearing G of thepump housing 3, and the D-cut portion 11A in a lower end of the rotatingshaft 11 is inserted to the segmental hole 8B of the impeller 8 so as tobe engaged.

[0057] Accordingly, when the electric power is fed to the armature 10via a connector 2E and the electric motor M is rotated, the impeller 8is synchronously rotated by a rotating force applied from the rotatingshaft 11. The fuel is sucked into the pump chamber 7 from the fuelinflow passage 6 in accordance with the rotation of the impeller 8within the pump chamber 7. The fuel pressured increasedly within thepump chamber 7 is supplied into the motor chamber 9 via the dischargehole 5, and the fuel within the motor chamber 9 is supplied toward anexternal fuel injection valve (not shown) via the fuel discharge passage2C.

[0058] In this case, in accordance with the fuel pump of the presentinvention, the discharge hole 5 is provided with the fuel holdingfunction obtained by the fuel film caused by the surface tension of thefuel at a time when the fuel pump is stopped.

[0059] In other words, when the fuel pump is stopped, the fuel remainingwithin the pump chamber 7 is discharged to the external from the fuelinflow passage 6 by the air flowing into the pump chamber 7 from the airbleeding hole 4D, and the pump chamber 7 becomes empty.

[0060] Paying attention to the discharge hole 5 in the state mentionedabove, the lower end 5A of the discharge hole 5 is open so as to face tothe pump chamber 7 in which no fuel but air exists, and on the otherhand, the fuel continuous with that in the motor chamber 9 exists in thedischarge hole 5, whereby the fuel film F serving as the fuel holdingfunction applied by the surface tension of the fuel is formed in thelower end 5A of the discharge hole 5. This structure can be understoodby FIG. 3.

[0061] Further, since the fuel film F serving as the fuel holdingfunction is formed in the discharge hole 5, the air existing within thepump chamber 7 can not flow into the motor chamber 9 via the dischargehole 5 due to the resistance of the fuel film F, and the replacingoperation between the air and the fuel within the motor chamber 9 is notcarried out. Accordingly, the fuel reserving within the motor chamber 9is inhibited from being discharged to the outside via the discharge hole5, the pump chamber 7 and the fuel inflow passage 6.

[0062] In this case, it is necessary that the discharge hole 5 secures adesired pump discharge amount in addition to the fuel holding functionmentioned above. For example, a fuel pump for a compact car of about 660cc engine displacement requires a pump discharge amount of 60 L/H. Inthe case of using the impeller 8 having a diameter of 33.6 mm, athickness of 3.8 mm, and forty six blade grooves 8A, in the fuel pump,the fuel holding function caused by the surface tension of the fuel, andthe desired pump discharge amount can be obtained by setting atransverse cross sectional area of the discharge hole 5 to be 7.884 mm².

[0063] In this case, the numeric values mentioned above are only for oneembodiment, and the discharge hole can be set appropriately in view ofboth sides so as to have both the pump discharge amount, and the fuelholding function achieved by the fuel film formed by the surface tensionof the fuel.

[0064] As mentioned above, since the fuel film F serving as the fuelholding function is formed in the discharge hole 5, at a time ofstopping the fuel pump, the fuel within the motor chamber 9 does notflow out to the external even at a time when the engine is stopped, andit is possible to continuously reserve and hold the fuel within themotor chamber 9. Accordingly, in the case that the electric motor M isdriven at the time of restarting the engine from the engine stop statementioned above, it is possible to supply the fuel which is continuouslyreserved within the motor chamber 9, toward the fuel injection valve(not shown) via the fuel discharge passage 2C, as soon as the pumpchamber 7 having a far small volumetric capacity is filled with thefuel, so that it is possible to restart the engine with no time delay.

[0065] Further, the fuel film F formed in the discharge hole 5 is notchanged even in the case that the arrangement state of the fuel pump ischanged. It is possible to always reserve and hold the fuel within themotor chamber 9 at a time when the fuel pump is stopped, withoutrelation to the arrangement state of the fuel pump.

[0066] Accordingly, it is possible to always restart the engine with notime delay, without relation to the arrangement state of the fuel pump.

[0067] Further, in accordance with the present invention, since the fuelfilm F formed in the discharge hole provided in the fuel pump isutilized as the fuel holding function, it is not necessary to use newparts.

[0068] Accordingly, it is unnecessary to increase the number of theparts and the number of the assembling man-hour, it is unnecessary tocheck to warrant a durability caused by increasing the constitutingparts, it is extremely easy to apply to the conventional fuel pump andit is possible to inhibit a manufacturing cost from being increased.

[0069] Further, the lower end 5A of the discharge hole 5 is open to thelower surface 3C of the pump housing 3 with the step portion 5B expandedsideward, and the impeller 8 arranged within the pump chamber 7 is notbrought into contact with the fuel film F at a time when the fuel film Fis formed in the lower end 5A of the discharge hole 5 due to the surfacetension of the fuel, whereby it is possible to more securely form thefuel film F.

[0070] In the present embodiment, the step portion 5B is provided to bedepressed in the upper side from the upper portion 3G of the fuel flowpassage 3D in the housing 3, and this structure is clearly shown in FIG.3.

[0071] In brief, the step portion 5B performs the function of preventingthe fuel film F formed in the lower end 5A of the discharge hole 5 frombeing in contact with the other members.

[0072] Further, in the case that the opening area of the discharge holeis made smaller toward the front side in the rotational direction A (aclockwise rotational direction in FIG. 2) of the impeller 8, it ispossible to further securely form the fuel film F.

[0073] The opening area of the discharge hole 5 is formed tapered towardthe front side in the rotational direction A in FIG. 2, the fuel film Fcaused by the surface tension of the fuel is first formed in the leadingend portion of the tapered discharge hole 5, and the fuel film F isformed by growing toward the rear end portion of the discharge hole 5.In other words, the fuel film F formed at an early stage in the leadingend portion of the tapered discharge hole 5 is immediately expanded likeas rippling all over the discharge hole 5.

[0074] Further, in the case that the step portion 5B mentioned above isformed in the similar shape to the shape of the discharge hole 5, anapproximately even escape portion B can be formed for the fuel film Fformed in the lower end 5A of the discharge hole 5, so that it ispossible to further securely inhibit the impeller 8 from being broughtinto contact with the fuel film, and it is effective to form and holdthe fuel film F.

[0075] Further, in accordance with the structure mentioned above, it ispossible to form a cast pin corresponding to the discharge hole 5 in asimilar shape to a cast pin corresponding to the step portion 5B, at atime of forming the pump cover 4 in accordance with an injectionmolding, so that it is possible to easily manufacture the cast pins.

[0076] As mentioned above, in accordance with the Wesco type fuel pumpof the present invention, since the fuel holding function for inhibitingthe air from flowing into the motor chamber from the pump chamber due tothe surface tension of the fuel at a time when the fuel pump is stopped,is provided in the discharge hole provided in the pump housing whichcommunicates the pump chamber with the motor chamber, the fuel reservedwithin the motor chamber is not discharged into the fuel tank throughthe fuel inflow passage on the basis of the fuel film which is formed inthe discharge hole by the surface tension of the fuel and has the fuelholding function, at a time when the engine is stopped and the fuel pumpis stopped, even in the case that the fuel pump is arranged within thefuel tank, and the fuel liquid surface within the fuel tank is lowerthan the opening of the fuel inflow passage formed in the pump cover.

[0077] Accordingly, it is possible to immediately restart the enginewith no time delay at a time of restarting the engine, and it ispossible to stably restart the engine even in the different arrangementstates of the fuel pump.

[0078] Further, since the discharge hole itself is provided with thefuel holding function, it is possible to inhibit the manufacturing costfrom being increased without requiring any specific new parts, and it ispossible to extremely easily apply to the conventional fuel pump.

[0079] Further, in the case that the lower end of the discharge hole isopen to the lower side of the pump housing with the step portion, thefuel film formed in the lower end of the discharge hole is not broken bythe other members, and it is possible to stably form and maintain thefuel film.

[0080] Further, in the case that the opening area of the discharge holeis formed smaller toward the front side in the rotational direction ofthe impeller, it is possible to immediately and securely form the fuelfilm in the lower end of the discharge hole.

[0081] Further, in the case that the step portion formed in the lowerend of the discharge hole is formed in the similar shape to the shape ofthe discharge hole, it is possible to form the even escape portion withrespect to the lower end of the discharge hole, it is possible tosecurely form and hold the fuel film, and it is possible toinexpensively form the step portion.

What is claimed is:
 1. A Wesco type fuel pump comprising: a pump chamberwhich is formed of a pump housing and a pump cover covering the pumphousing; an impeller which is rotatably arranged within the pumpchamber, is rotated by an electric motor within the motor chamber, andis provided with a plurality of blade grooves communicating the top andback sides in an outer periphery thereof; and a discharge hole which hasa fuel flow passage provided in a depressed shape in a peripheraldirection along the blade grooves of the impeller on a lower surfacefacing to the pump chamber of the pump housing, and is formed in aterminal end portion in a rotational direction of the impeller so as tocommunicate the pump chamber with the motor chamber, wherein saiddischarge hole (5) is provided with a fuel holding function ofinhibiting air from flowing into the motor chamber (9) from the pumpchamber (7) on the basis of surface tension of the fuel, at a time whenthe fuel pump is stopped.
 2. A Wesco type fuel pump as claimed in claim1, wherein said discharge hole is open in the lower surface (3C) of thepump housing (3) with a step portion (5B) facing to the pump chamber(7).
 3. A Wesco type fuel pump as claimed in claim 1, wherein an openingarea of said discharge hole is made smaller toward the front side in arotational direction of the impeller.
 4. A Wesco type fuel pump asclaimed in claim 2, wherein said step portion is formed in a similarshape to the discharge hole.